Department of Medicine, University of Illinois at Chicago, 60612, USA.
Biochem J. 2013 Sep 1;454(2):201-8. doi: 10.1042/BJ20130282.
NAC (N-acetyl-L-cysteine) is commonly used to identify and test ROS (reactive oxygen species) inducers, and to inhibit ROS. In the present study, we identified inhibition of proteasome inhibitors as a novel activity of NAC. Both NAC and catalase, another known scavenger of ROS, similarly inhibited ROS levels and apoptosis associated with H₂O₂. However, only NAC, and not catalase or another ROS scavenger Trolox, was able to prevent effects linked to proteasome inhibition, such as protein stabilization, apoptosis and accumulation of ubiquitin conjugates. These observations suggest that NAC has a dual activity as an inhibitor of ROS and proteasome inhibitors. Recently, NAC was used as a ROS inhibitor to functionally characterize a novel anticancer compound, piperlongumine, leading to its description as a ROS inducer. In contrast, our own experiments showed that this compound depicts features of proteasome inhibitors including suppression of FOXM1 (Forkhead box protein M1), stabilization of cellular proteins, induction of ROS-independent apoptosis and enhanced accumulation of ubiquitin conjugates. In addition, NAC, but not catalase or Trolox, interfered with the activity of piperlongumine, further supporting that piperlongumine is a proteasome inhibitor. Most importantly, we showed that NAC, but not other ROS scavengers, directly binds to proteasome inhibitors. To our knowledge, NAC is the first known compound that directly interacts with and antagonizes the activity of proteasome inhibitors. Taken together, the findings of the present study suggest that, as a result of the dual nature of NAC, data interpretation might not be straightforward when NAC is utilized as an antioxidant to demonstrate ROS involvement in drug-induced apoptosis.
NAC（N-乙酰-L-半胱氨酸）常用于鉴定和测试 ROS（活性氧）诱导剂，并抑制 ROS。在本研究中，我们发现蛋白酶体抑制剂的抑制作用是 NAC 的一种新活性。NAC 和另一种已知的 ROS 清除剂过氧化氢酶都能类似地抑制与 H₂O₂相关的 ROS 水平和细胞凋亡。然而，只有 NAC，而不是过氧化氢酶或另一种 ROS 清除剂 Trolox，能够阻止与蛋白酶体抑制相关的作用，如蛋白质稳定、细胞凋亡和泛素缀合物的积累。这些观察结果表明，NAC 具有作为 ROS 抑制剂和蛋白酶体抑制剂的双重活性。最近，NAC 被用作 ROS 抑制剂来对一种新型抗癌化合物哌泊隆进行功能表征，导致其被描述为 ROS 诱导剂。相比之下，我们自己的实验表明，该化合物表现出蛋白酶体抑制剂的特征，包括抑制 FOXM1（叉头框蛋白 M1）、稳定细胞蛋白、诱导 ROS 非依赖性细胞凋亡和增强泛素缀合物的积累。此外，NAC 而不是过氧化氢酶或 Trolox 干扰了哌泊隆的活性，进一步支持哌泊隆是一种蛋白酶体抑制剂。最重要的是，我们表明 NAC 而不是其他 ROS 清除剂直接与蛋白酶体抑制剂结合。据我们所知，NAC 是第一个已知的直接与蛋白酶体抑制剂相互作用并拮抗其活性的化合物。总之，本研究的结果表明，由于 NAC 的双重性质，当 NAC 被用作抗氧化剂来证明 ROS 参与药物诱导的细胞凋亡时，数据解释可能并不简单。
